Abstract
Membrane fouling properties and different physical cleaning methods for forward osmosis (FO) and reverse osmosis (RO) laboratory-scale filtration systems were investigated. The membrane fouling, with respect to flux reduction, was lower in FO than in RO when testing an activated sludge effluent. Cross-flow velocity, air-scouring, osmotic backwashing and effect of a spacer were compared to determine the most effective cleaning method for FO. After a long period of fouling with activated sludge, the flux was fully recovered in a short period of osmotic backwashing compared with cleaning by changing cross-flow velocity and air-scouring. In this study, the osmotic backwashing was found to be the most efficient way to clean the FO membrane. The amount of RNA recovered from FO membranes was about twice that for RO membranes; biofouling could be more significant in FO than in RO. However, the membrane fouling in FO was lower than that in RO. The spacer increased the flux in FO with activated sludge liquor suspended solids of 2,500 mg/L, and there were effects of spacer on performance of FO–MBR membrane fouling. However, further studies are required to determine how the spacer geometry influences on the performance of the FO membrane.
Highlights
In pressure-driven membrane processes, such as microfiltration (MF), ultrafiltration (UF), nanofiltration and reverse osmosis (RO), water is filtered mainly by using hydraulic pressure as a driving force
Mi & Elimelech ( ) reported that the fouling observed in forward osmosis (FO) was more reversible than that in RO, and they believed the hydraulic compaction was less on the surface of FO membranes
A number of physical cleaning methods were compared in order to discover the most effective cleaning method to restore the performance of FO
Summary
In pressure-driven membrane processes, such as microfiltration (MF), ultrafiltration (UF), nanofiltration and reverse osmosis (RO), water is filtered mainly by using hydraulic pressure as a driving force. The control of fouling still remains a challenge for water treatment industries, and researchers have developed novel filtration processes and membrane modifications for more efficient filtration systems. There has been growing interest in osmotically driven membrane processes, such as forward osmosis (FO), as highly efficient, sustainable processes that can replace the pressure-driven membrane processes (McCutcheon et al ; Lutchmiah et al ). In the pressure-driven membrane process, water is filtered by applying hydraulic pressure; in the FO process, water is filtered by using osmotic pressure as the driving force. The main advantages of the FO process are no need for hydraulic pressure and a high removal rate exhibited for a wide range of contaminants (Cath et al ), and lower susceptibility to membrane fouling than pressure-driven membrane
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